A sensor is described, for example, in German Patent No. 195 03 236. In surface micromechanics, sensors of this type are manufactured from a multilayer semiconductor substrate. In this context, in a first semiconductor layer of the substrate, a movable mass is formed through patterning, the mass being mounted on support blocks of the substrate through a plurality of spring elements also delineated out of the semiconductor layer. The movable mass has electrode patterns which, together with further, fixed electrode patterns configured in the semiconductor layer, form capacitors. A deflection of the movable mass in opposition to the tensional force of the spring elements resulting from inertial and/or Coriolis forces changes the capacitance of the capacitors. The capacitance changes are used to determine acceleration or rotational speed.
The known sensors use U-shaped spring elements having two arms running parallel to each other, the arms projecting from a common connecting bar. The spring elements are designed so that they have slight rigidity in the direction of detection and great rigidity in the other two spatial directions. As a result, interfering influences can be suppressed. It has proven to be disadvantageous in the known sensors that the deflection of the movable mass perpendicular to the semiconductor layer resulting from a shock or impact leads to a fracture of the spring elements, which in this direction do not have great load-bearing capacity. Although it is possible to limit the deflection of the movable mass in the plane of the semiconductor layer using limit stops, the deflection of the movable mass perpendicular to the plane of the semiconductor layer cannot be prevented, since in this direction no limit stops can be formed for production technical reasons. In conventional sensors, therefore, a fracture in the spring elements in response to impact or shaking stresses cannot be avoided.
In the sensor according to the present invention, the disadvantages of the related art are avoided. This is achieved through the fact that the end segments of the arms of the at least one spring element in the plane of the semiconductor layer in the longitudinal direction of the arms are initially directed (shaped) so as to be bent away from each other and then are directed so as to be bent towards each other, joining each other in a central bent area. In this manner, in the connecting area of the two arms, curvatures are formed, which, in response to a deflection of the movable mass perpendicular to the semiconductor layer, reduce the maximum stresses arising in the material to values at which the risk of fracture of the spring elements can be significantly reduced. In addition, the spring element in the detection direction, running parallel to the semiconductor layer, has the necessary slight rigidity, so that a reliable deflection of the movable mass can be assured even in response to small accelerations. Advantageously, the geometry of the at least one spring element does not require any additional production expense in the manufacture of the sensor. As a result of the geometric configuration of the spring element, the reliability and the service life of the sensor are increased.
An exemplary embodiment of the present invention that is particularly advantageous is one in which the end segments of the two arms of the spring element joined to each other form a connecting area, which is composed of a plurality of spherically bent areas.